Generally, writing instruments are classified into a stationary type writing instrument, in which a pen core is stationary and is covered with a cap, and a retractable writing instrument. The retractable writing instrument is classified into a rotating type writing instrument, in which a nib is moved along a spiral moving path by rotating part of a casing so that part of the nib is extractable from or retractable into the casing, a knock type writing instrument, in which, when part of a casing is pushed, a nib is extracted from the casing or is retracted into the casing using a spring, and a slide type writing instrument, in which a nib is extracted from or retracted into a casing by siding.
Here, the retractable writing instrument has an advantage in that it is not necessary to use a separate cap. However, because a nib hole, through which the nib is extracted from and retracted into a casing, is formed in an end of the casing, there is a disadvantage in that it must be limitedly used only for writing instruments using ink having low volatility or nonvolatile ink, for example, oil-based ink.
On the other hand, in the case of writing instruments using ink having high volatility, for example, marker pens, correction pens, water-based pens, highlighters, etc., as well as being inconvenient because a cap must be used, if a nib is exposed to air for a long time, the ink in the nib dries out, thus reducing the lifetime of the writing instrument, or spoiling it.
In an effort to overcome the above problems, a lot of research on techniques for preventing ink and for protecting a nib in writing instruments that use liquid or semi-liquid ink or volatile or nonvolatile ink has been conducted.
A representative technique for preventing a nib from drying out and for protecting the nib was proposed in Japanese Patent No. 1987-0012570, which is entitled ‘CAPLESS WRITING INSTRUMENT HAVING DRYNESS PREVENTION DEVICE’. In the writing instrument according to this technique, when a pushing part is pushed, a cover, which covers a nib, is opened by the tensile force of an elastic cord. In this state, when the pushing part is pushed again, the cover is closed to seal the nib, thus preventing ink from drying out. However, because the tensile force of the elastic cord is used to open and close the cover, the operation of opening or closing the cover cannot be rapidly conducted, and the durability is insufficient. Furthermore, there is a disadvantage in that the sealing ability of the cover, which openably closes a nib opening, is very low.
Meanwhile, another conventional technique pertaining to a retractable writing instrument was proposed in 1999 in Korean Utility Model Registration No. 174279, entitled ‘NIB DRYING PREVENTION DEVICE’. In this technique, when a pushing part of the retractable writing instrument is pushed, the nib is advanced forwards and protruded outside through a slit in a rubber packing, thus enabling the use of the writing instrument. When the pushing part is released or pushed again, the nib is returned to its original position, and the slit is sealed by the elastic force of the rubber, thus preventing the ink from drying out.
However, in the case where the writing instrument is frequently used for a long period, the rubber packing having the slit may be plastically deformed. Furthermore, it is difficult to seal the pushing part that undergoes sliding movement. Therefore, the sealing ability of the writing instrument is relatively low.
Another conventional technique was proposed in Korean Patent Application No. 65693 in 2000, entitled ‘WRITING INSTRUMENT HAVING NON-SEPARABLE TYPE ELASTIC CAP’. In this technique, a slit, through which a nib passes, is formed in an elastic cap at a position adjacent to the nib, and the elastic cap is in close contact with a guide hole of a writing instrument which is formed at a position opposite the slit. When the cap is moved backwards, the nib is exposed outside to allow the use thereof. When the cap is advanced forwards, the writing instrument enters a state in which ink is prevented from drying out. In addition, the intermediate part of the cap has a shape corresponding to an associated part of the casing of the writing instrument.
However, in the case of the technique of No. 65693, because the nib is extracted or retracted through the slit, the part of the cap around the slit is easily stained with the ink of the nib. Furthermore, because the part of the cap around the slit is compressed by a separate assistant member, such as a rubber ring having predetermined elasticity, the nib may be damaged through contact with the cap around the slit. In addition, there is a disadvantage of low durability. As well, because the rubber ring that is provided around the slit is exposed outside, the rubber ring may be damaged by contact with other objects. Moreover, in the case where the writing instrument is frequently used for a long period, the part of the cap around the slit may be deformed, thus reducing the sealing ability.